Device comprising a mercury cathode tube for interrupting electric currents of high voltage



July 13, 19 J. G. w. MULDER ET AL 5, 7

DEVICE COMPRISING A MERCURY CATHODE TUBE FOR INTERRUPTING ELECTRIC CURRENTS I OF HIGH VOLTAGE V Filed April 17, 1946 5 Sheec'-Sheet 1 July 13, 1948. w MULDER ETAL" 2,445,075

DEVICE COMPRISING A MERCURY CATHODE TUBE FOR INTERRUPTING ELECTRIC CURRENTS OF HIGH VOLTAGE v Filed April 1'7, 1946 3 Sheets-Sheet 2 Jfi y J. G. w. MULDER ETAL 2 9 DEVICE COMPRISING A MERCURY OATH-ODE TUBE FOR INTERRUPTING ELECTRIC CURRENTS OF HIGH VOLTAGE Filed April 17,1946 3 SheetsSheet 3 ficult to interrupt the Patented July 13, 1948 DEVICE COMPRISING A MERCURY CATH- onn TUBE FOR INTERRUPTING ELEC- TRIC OURRENTS OF HIGH VOLTAGE Johannes Gijsbertus Wilhelm Mulder and Albert.

Bouwers, Eindhoven, Netherlands, assignors, by

mesne assignments, to Hartford National Bank and Trust Company, Hartford, Conn., as trustee Application In the April 17, 1946; Serial No. 662,794 Netherlands April 12, 1941' Section 1, Public Law 690, August 8, 1946 Patent expires April 12, 1961 The invention relates to a device for translating electric currents of high voltage, and particularly to apparatus which has incorporated in .it a mercury cathode current-converting tube comprising an ignition electrode and an auxiliary anode for producing and maintaining respectively an electron discharge. y

With such devices, which are utilized more particularly as direct current-alternating current inverters for high voltage, it is in general very difdischarge at any time at which this discharge still has a substantial current intensity. More particularly at very high anode voltages it is inconvenient in practice to reduce the anode current to zero even for a short time only or to lower the anode voltage to approximately zero value. Moreover, a particularly great possibility exists for the extinguished discharge to be reignited by the residual ionisation still present prior to the prescribed interruption time.

It is known already, for example, from the French patent specification 844,414 to arrange a set of auxiliary electrodes and. an ignition electrode of high resistance inside a screen in such manner that these members communicate with the main discharge chamber and with the main anode arranged therein by means of holes in the edge of the screen at the level of the surface of the mercury. In this case the main discharge is ignited owing to the fact that the cathode spot of the auxiliary discharge, which, spot is formed inside the screen,

is drawn to the exterior by the anode field or at least is divided and is partly drawn to the exterior. Tubes of this type'are not suitable for use at very high voltages since the main anode is exposed without any protection to the liquid and vaporous mercury which is slung from the cathode spot into the main discharge chamber as soon as the cathode spot is drawn to v the exterior of the screen.

The invention has for its object to realize with the above described devices for interrupting currents of high voltage such a construction and such an operation that the above-mentioned drawbacks are avoided, more particularly in such man- 7 Claims. (Cl. 250 -2*1L5) 2 her that the extinction of the discharge takes place with greater reliability and that the main discharge path is kept, even afterextinction, as much as possible free of disturbing ionisation.

According to, the invention, for this purpose not only the auxiliary arc, the ignition electrode and the auxiliary anode but also the whole of the operative surface of the cathode are provided withina spacechamber which is closed for the major part, the arrangement being such that substantially all the mercury originating from the cathode remains within this chamber while the maindischarge and the auxiliary discharge are extinguished by simultaneous voltage impulses of steep wave front on the main and auxiliary anodes, owing to Which the cathode spot in' the closed'space is loosened from the cathode mercury.

In the above described manner the certainty of the extinction of the main discharge is greatly promoted by the fact that the actions of the extinguishing impulse on the main and auxiliary discharges support one another provided that they act simultaneously on these discharges. This is attended with a particularly satisfactory deionisation of the main discharge in consequence of the fact that in all circumstances the cathode spot is screened while in thiscase it is not necessary to arrange particular extinguishing grids in the discharge path, all the drawbacks inherent to these members, such as a high value of the arc voltage dueto the presence of great contractions in the discharge path or the production of appreciable grid currents due to the large operative surface of thegrid, being thus avoided.

It is possible to utilize a deviceaccordin'g to the invention as a switch for direct currents of high voltage or as an inverter tube, i. e.,'for converting direct current of high voltage into alternating current. These two applications are particularly important for the solution of the probleni of the transfer of energy over a large'distance by means of high-voltage direct current. The first-mentioned application makes it possible to construct a switch or high power of particularly small dimensions and, while suppressing the chamber which communicates with the two other chambers through the intermediary of narrow connecting pieces and which prevents mercury particles which originate from the cathode chamher from reaching the main anode along the discharge path, a particularly high blocking capacity in the negative voltage phase of the main anode I being thus obtained. I i

In certain cases it may, however, be advantageous to make no use of a separate condensadirection, which favours the dissipation of heat from the screen to a high extent.

The invention will be explained more fully with reference to a 'few examples of tubes and wiring diagrams according to the invention which are diagrammatically shown in the drawings.

Figs. 1, 2 and 3 represent diagrammatically and in section constructions of tubes for devices according to the invention.

Figsxi and 5 represent wiring diagrams of extinguishing devices according to the invention.

Fig. 1 represents a current-converting tube whose discharge vessel consists of two parts I and 2 which are connected to one another through the intermediary of a metal connecting tube 3 hermetically sealed thereto and of a helically wound glass tube it. The part I contains a mercury cathode 5 which is in contact with an ignition electrode 6 of semi-conductive material which is led to the exterior at 1. In the upper it half of l is arranged an auxiliary anode 8 which entertains the auxiliary arc as soon as the ignition chamber and to construct thedischarge tube T in such manner that the operative surface of the cathode and the electrodes for producing; and entertaining the auxiliary discharge areenclosed by a screen of a material of satisfactory thermal conductivity, said screen, or at least part thereof, beingimmersed in the cathode mercury, which is preferably provided with a cooling device. It is advantageous to select in this case a construction such that the heat developed in the discharge substantially delivered to the surroundings through the intermediaryof the screen and the cathode mercury. It is frequently possible to withdraw in this wayso much heat from the discharge path that the complication of a separate condensation chamber can be avoided.

According to a particularly advantageous embodiment of the inventive idea use is made of a current-converting tube wherein the operative surface of the cathode and the electrodes for producing and entertaining the auxiliary discharge are surrounded by a substantially cylindrical screen which is partly immersed in the cathode mercury and which, if desired, may be provided i1f1its uppermost aperture which acts as a passagefor the main discharge, with controlling Y members whilst the bell-shaped main'anode'surrounds the upper portion of this screen; the arrangement-beingsuch that nowhere within the tube between the anode and these parts are, available uninterrupted paths of electrostatic lines of force which are longer than approximately half the length of the free paths of the electrons at the operating pressure of the tube. In this Way substantially-the whole of the discharge path is enclosed by a screen of satisfactory thermal transmission, Whilst a construction of particularly small dimensions and of high blocking capacity in the non-conductin phase is obtained,

, According to another form of construction of a current converting tube for a device according to the invention, the screen inside of which are present the operative cathode surface and the electrodes for producing and entertaining-the auxiliary discharge, is arranged coaxially in the cylindrical discharge vessel of the t'ube at a small radial distance therefrom whilst the anode is arranged in a similar manner in the extension of this screen and the upper passage aperture of the screen is covered, with a small intervening .spaceby the anode front whichis perpendicular to the axis of the tube. Thus the screen is substantially not covered by the anode in the radial tionis brought about by the electrode 6. As the ignition electrode may also be utilized a capacitative electrode, for example a thin-walled ball of quartz which is partly immersed in the mercury and 'which is internally provided with a conductive coating which is led to the exterior so as to be screened. In the upper half of the part 2, which is divided in two at approximately half its height by a ring IE or chrome-iron, isarranged a main anode I 6 which is hermetically lied to the exterior at II. On either side of the metal connecting tube 3 are provided funnel shaped pieces l0 and H for guiding the main discharge between the cathode 5 and the anode (fill-and for protecting the sealing-in' zones of the 'itube 3. Moreover, a positive or negative voltage maybe applied to the aggregate 3- |0-H in order'to facilitate the ignitionof the'arc or to increase the blocking capacity in the non-conducting phase. Inside the annular wall portion i2 is arranged a body i3 whose lower end has the shape of a funnel and which serves, as does the previously described body lo snto uide the discharge towards the mainyanodelfi and to protect the seals of the ring l2; The body [3 terminates at its upper end in a hollow profiled rim l5 and is internally provided with adiaphragm M and with radial faces l9. Qnlythe central portion of the anode front isle ft free by the rim l5 and the diaphragm h-l which pr event forthe rest the formation ofuninterrupted paths of linesof force which are longer than half the length of the free paths of the eleotrons,'j which paths otherwise might be formed betweenjhe anode surface and adjacent conducting parts of other. potential, the blocking capacity of thetube being thus greatly enhanced. The. anode.'terminal I! has secured to it a bell-:shapedjscIQen l8 which prevents undesirable concentration of electrostatic lines of force on the backside; f the anode.v The operation of thejtube is as follows; after a cathode spot has been formed 'by. means of the electrodes, an auxiliary discharge is produced between the mercury cathode 5 and the auxiliary anode 8, owing to which the,.cathodejspot is maintained so that as the case' maybe'with the aid of suitablepotentials appliedto the electrodes 3 and 3, a main discharge. may be formed on the anode l6. Thejcathode, spot alwaysremains in this case insideithe vessel I whileflmercury passing through 3 in the form of vapour is condens-ed in the lower portion of the vessel 2 and,

can flow.- back throughthe glass tube! to -the mercury cathode -5. -As soon as, inaaccordance with 'the invention, voltage impulses with a steep wave-front: are applied simultaneously 130 42118- auxiliaryranode 8 and the main anode l.6,-'the cathodespot at the surfacelof the cathode dis appears due to the fact that the anode voltages of the main and auxiliary dischargesxapproximate for a short time to the zero value: or attain this value.- Owing to the construction. of the tube no i ionization occurs. 1 during the: blocking phase in .thepart2 of the dischargevesselwwhilst mercury originating from the cathode scompart ment is condensed in the'lower portion of 2 and cannot reach the main anode l6. Inconsequence thereof "the tube: functions in a .very 'relia'ble manner even at unidirectional voltages 'of' 20,000 volts A tube of the above-mentioned dimensions, "is suitable for a current intensity of "6 amp. R. MLS. whilst in the case of larger dimensions-it is very well possible to extinguish tens 'of amperes': I

Fig. 2 shows a'd-iagramm-ati'cal sectioned at cur rent converting tube comprising a dischargewess'el*20 of ,glass which contains-a mercurycath'ode 2 land a main anode 22. In the mercury cathode is provided a semi-conductive"ignition electrode 23' which is ledout of the tube-at the low'e'nen'd thereof'at 25. Above the ignition ele'ctrod'eis arranged an annular auxiliary anode whichis likewise taken out of the tube' at the lower-end at 263 With this construction of thetube house is made of a separate condensation chamber but for the'transmission of the heat of condensation and'of the heat due to energy losses use is made ofa cylindrical screen 21 the lower-end of which is immersed in the mercury and which surrounds the operative surface of the-cathode, the ignition electrode and the auxiliary anode. This screen consists-cf a material of satisfactory thermal: conductivity and is provided with'a plurality of radial iac'es'28 which have large surfaces of contact with the cathode mercury and which assist in-the transmission of heat from the screen 21 to 'the mercury 2! by which the heat is delivered through the wall of the vessel 20 to the exterior, if desired with the aid of an artificial cooling device; m'lhe upper portion of the screen 21 is surrounded :by the bell-shaped anode- 22 the relative position of this anode,- of the cylindrical portion-ofxt'he screen 21 and of the flat portion thereoLwhich is bent down'at its outer edge is such that within the tube between the anode 22 and other members whose potentials are different-from that of the latter anode uninterrupted pathsvof lines-of forceof more than approximately half the length of the free paths of the electrons are avoided at the-operating pressure of the tub-e. Inside the screen and at the upper end. thereof is arranged a "grid-shaped member at with the aid of which, by applying a positive'voltage thereto, the ignition'of themain discharge or, by applying anegative voltage, the extinction or the continuance thereof :can' be promoted. At thelower end of thetube the grid is led to the exterior at 3 l and thecathode2l at 32. The lower portion ofthe tube is surrounded by a cooling jacket "33 which is provided withaninlet tube 34 and an'outlet tubew35 and through which may circulate-any desired gaseous or liquid cooling medium.

The method of operation of the above-described tube: corresponds to that of the tube according to Fig 1. -With.respect to the latter it offers, however, the advantage of smaller dimensions for of deduced'susceptibility of damages Neither inl the -constnuction according toiig. 3 is made use of re separate condensation vessel. The cylindrical dischargezvessel ill-contains cathode mercury 4| with-a supply conductor-42, a main anode 4 3 lwithx a supply wire lka semi-conductive ignition electrodelitwith a supply wire 46 which is led to 1 the 1' exterior: in aninsulated manner at the lower encl of the tube and two auxiliary anodes 41 and 48 with supply wires 50 vand 49' which are ledto'the'exteriorat the lower end" The cathode chamber is surrounded in this case by a screen 5| provided-with radial coolingwanes 52, said screen- "being'immersed'in the cathode mercury in a similar manner to that shown in Fig. 2. The lower--portion pr the screen': 5| hasa frustoconical, the upperportion,- however; a cylindrical shape} the latter portion =being at a very short distahce from 'the wall' ofthe vessel 40 so that hereagain a satisfactory transmission of heat to theexterioriis possible.- The top of the screen is flat-and: at o; veryi'sm'all distance therefrom and parallel thereto is located the front face of the anode which is cylindrical on the outside and which 'is likewise arrangedwithin the discharge vessel at a very small distance therefrom"; owing to which also in thi's case uninterrupted paths of lines of *force 0f excessive length are avoided. The auniliary:anodes =41 and 48 arranged in suc- 1 cessionpromote the" reliability of the ignition' of the main discharge-"throughthe' aperture '53 on the anode; Owing to-th'e use-of a plurality of auxiliary anodes we" are at liberty to take -th'e screen=5 l of such'height'that no mercury'orig'i nating from the cathode spot can pass at all through the aperture '53but'that it deposits previously" on the "wall or the screen 5| and flows back to the "cathode 4]: For the purpose of cooling the lat'ter'th'elower tube portion is surrounded by 'a cooling jacket 54 provided withtubes- 55 and 56 for 'thesupply and the discharge respectively of a gaseous or liquid cooling medium. v v "Fig; '4 representsdiagrammatically an' extinguishing device comprising a current-converting tube wth a mercurycathode which may form part v of a direct current alternating" current inverter tube according to theinven'tion; of thetube v60 is connected onth'e one hand; to an inverter circuit-arrangement diagrammatically denoted by 62 and on the other hand'via the primary winding 630i a transformer 64 tofthe incandescentcathode 650i a relay tube 66.] The grid 61 ofthis tube has connected'to'it, through the intermediary of a resistance 68, the secondary I69 of a peak voltage transformerjflfl whose primary winding H Y isfconnected' to an alternating .-current supply I2. l The anode '13 'of the relay tube 66 is connectedthroughtheintermediary of the series connection of a resistance .14 and a source-of unidirectional voltage 15 and, parallel thereto,-vla a condenser" t o that terminal of the-primary I winding 63 which is remote from the incandescent cathode '65, said terminal of the primary-winding being also connectedto the mercury catho'dei l of the current-converting tube.-- Withevery positive impulse on the grid 61 the-condenserlfi is abruptlydischarged via the discharge-, path-of the relay tube so-that in the secondaryzwinding :11 e: the-transformer 64 are set up vol-tage'impulses of'steep wave-front which are supplied throughacondensers lfl and 19 to the main'anodeiw and the auxiliary anode-lil of the cur-rent convertingtube; the latter electrode having'r-a uni-directionarwioltage::applied to sit in t-he 5D.rbem cminvertersystem. 'Ihe -said impulses produced at the ifreq'uencyzof': the: controlling alternating current mains; for example 50 cycles,

and thustheanod'e's 80 and 8l acquire,atleast ior-ashort time, a negative or a lowipositive or zero potential with respect to the-,cathodeand this during a period oftime which is vsufiiciently long to cause the suppression of the cathode spot and therefore of the currentinthecurrent converting tube 60, for'exampleduring 10-. seconds. Itisihighly important that the impulses should besupplied to the anodes 8U and8 I exactlysimul- 'tan'eously since' otherwise the :reliability of; the extinction of the discharge is greatly reduced. The main'and auxiliary'discharges'of the'tube .60 are periodically produced by the ignition elec- .trode82 which is supplied by a source of peak voltage 83in synchronism'with the source of cur- :rent 12. The periodicsiniultaneous extinction .of mainand auxiliary anode currents" is synchronously brought about each time by means of the above-described .tcircuit-arrangementj according toithe invention; y .Fig; I5'repres'ents'..one'.form of construction of the extinguishing" device; .wherein the :iextinction frequency, is obtained by mechanical, agency by means of an interrupter contact 90 which is .driven by, a cam.9l"provided on a spindle. having a suitable speed of revolution. Similar parts-of the diagram are denoted bythesamenumerals as in the case of Fig.4. ,The interrupter contacts!) periodically closes, and interrupts the current from abattery 92, which current flowsthrough the primary winding 93 Of a coil 3d. The point of interruption is bridged by a condenser 95. By

means of thi arrangement, which corresponds toa usually employed ignition device for explosion engines, voltages impulses off-steep 'wave front aredelivered to the terminals of the secondary winding 95 of the coil, said impulsesbeing supplied in'fthe mannerfofIFig'j4 through'the condensers l8 and la-to the-anodes 80 and Blof the mercury cathode tube. 60.' This arrangement is. also suitable for ajswitchin'g device for the interruption of uni-directional current of high. voltage, provided that theinterrupter contact 90, instead for being periodically actuated by the rotatin cam, is actuated only once ineach switchingroff operation, for" example', 1by means of a push-button, in which eventthe cathode 6| and the anode 80 act as terminals of the'directcurrent switch. a I H With aldevice accordingto the invention it is possible to interrupt uni-directional currents by means of the above described tubes and circuit arrangements in areliable manner at voltages of the order ofjmagnitude of 20,000 voltsland with current intensities of the order of magnitude of from 10 to 100 amperes.

'Whatwecl-aimist, f i 1. A high voltage mercury-arc tube comprising a cathode chamber, a liquid cathode, an ignition ,electrodea'ndfa keep alive electrode for main taining a gaseous atmosphere in said cathode chamber, an anode chamber spaced from and interconnected to said cathode chamber, an anode in said anode chamber; and an electrical con-ducting member adjacent said anode, the shortest distance between" said anode and said adjacent electrical conducting member bein less than one half the mean free path ofthe atmospherewithin the tube.- I

2. A high voltage mercury-arc tube comprising a cathode chambenaliquid cathode, an ignition electrode anda keep-alive electrode for maintaining a gaseous atmosphereinsaid cathodeelectrons in the 1 'c'h'amben: anode chamber: spaced? from a d interconnected 'by means of "a TCOIIStIlCtCd :passagewayto said cathode chambe'r, 4 an anode in said anode'chamb'er, and an electrical conducting member adjacent said :anode, the" electrical :dis-

tance between-said anode and said electrical conanode and said shield member" being iless than one half the'imean' free path ---of .the-'electrons within the atmosphere within the tube. r

4. A high 'voltagemercury-arctube comprising a. cathode: chamberya liquid cathode, an'igniti-on electrode and a keep-alive electrodexfor maintaining a gaseous atmosphere in said cathode chamber, anjyanode chamber'spaced from' and interconnected bymeahs'of aconstricted pasvsageway to said cathode chamber, ananode in said anode chamber, a shield member enclosing said ignition and said keep-alive electrodes,- said shield member being of good thermal'conductivityand partlyimmersedin said liquid cathode,

the shortest distance between. said anode and saidishield member being less than one'half the mean free path of the electrons within the-atmosphere within the tube, and fluid heat exchangin means to cool saidcathode chamber. Y I

i 5. A high voltage mercury-arc tube comprising acathode chamber, a liquid cathode, an ignitionelectrode and a keep-alive electrode-formaintaining a gaseous atmosphere in said cathode chamber, an anod-e'chamber, a constricted passageway interconnecting said cathode chamber to said anode chamber, shield members having good thermalconductivity connected to the ends of said passageway to aid condensation of the gas of said atmosphere, means to returncondensation from said anode chamber to said cathode chamber, an anodein said anode chamber, and an anode shield member arranged between said anode'and said cathode,the shortest jpathbetween said anode and said anode shield member being less than .one half the mean free pathof the electrons in the atmosphere within the tube.

6. A high voltage mercury-arc tubegcomprising an envelope, a. liquid cathode, .an ignition 'electrode, a keep-a1ive electrode for maintaining a gaseous atmosphere, 2. screen member and an anode in said envelope, a shield member enclosing said ignition electrode and saidkeep-alive electrode, said shield member being interposed between said anode and said cathode; being partly immersedin said liquid cathode and arranged to divide the interior of said envelope into a cathode chamber and an anode chamber, said shield member having an aperture beyond said screen. member and adjacent said a'n'odegthe shortest distance between said anode and said shield member being lessthan one half the mean free path of the electrons in the atmosphere within the tube, and fiuid'heat exchanging means applied to said envelope in the regionof said cathode; i a, I

7. .A high voltage mercury-arc tube comprising an envelope, a liquid cathode, an ignition electrode, a plurality of keep-alive electrodes successively arranged for maintaining a gaseous atmosphere and an anode in said envelope, a shield member enclosing said ignition electrode and said keep-alive electrodes, said shield member being interposed between said anode and said cathode, bein partly immersed in said liquid cathode and arranged to divide the interior of said envelope into a cathode chamber and an anode chamber, 10

the shortest distance between said anode and said shield member being less than one half the mean free path of the electrons in the atmosphere within the tube, and fluid heat exchanging means applied to said envelope i the region of said cathode.

JOHANNES GIJSBERTUS WILHELM MULDER. ALBERT BOUWERS. 

